High voltage particle accelerators using charge transfer processes



Nov. 14, 1967 CHARGE TRANSFER PROCESSES 2 Sheets-Sheet 1 Filed Oct. 6,1959 00000 0O0oooooo000o0oooo N VN,

1 1 I I l l I l I 1 1 I I I I 1.. 0000000000 0 0 000000|||||||lllllllllllxllllloooooooocoo o o o o 0 one N v- 4. 1967 R. J. VANDE GRAAFF 3,353,107

HIGH VOLTAGE PARTICLE ACCELERATORS USING CHARGE TRANSFER PROCES SES 2Sheets-Sheet 2 Filed Oct. 6, 1959 I I I l l I l I l I l l l l 1 l I l II l l l 1 l 1000000000000000 0000000 m NM United States Patent C) 3,353107 HIGH VOLTAGE PART ICLE ACCELERATORS USING CHARGE TRANSFER PROCESSESRobert J. Van tie Graaff, Lexington, Mass, assignor to High VoltageEngineering Corporation, Burlington,

Mass a corporation of Massachusetts Filed Oct. 6, 1959, Ser. No. 844,71116 Claims. (Cl. 328-233) This invention relates to new methods for theacceleration of charged particles to high velocity by means of highvoltages and charge transfer processes. The invention comprehends tandemcharge transfer processes wherein the charge state of the same beam ofcharged particles is changed more than once. In general there are threecharge states, namely a particle may be negatively charged or positivelycharged or neutral. The invention also comprehends tandem accelerationin which the available voltage is applied more than twice to the samebeam of charged particles so as to accelerate the same in at least threestages.

In the case of the usual type of electrostatic accelerator, positiveions are produced inside a high-voltage terminal and then accelerated toground in one stage of acceleration. In the case of the conventionaltype of tandem accelerator, negative ions are produced at ground, andthen accelerated to a high-voltage positive terminal. Within theterminal the swiftly moving negative ions are stripped of electrons,thus becoming positive ions, which then receive an additionalacceleration from the terminal to ground. Thus the particle beamreceives two stages of acceleration instead of one.

The principles and techniques used in such conventional tandemaccelerators have been originated and developed over many years and invarious laboratories. It is regretted that lack of space prevents fullacknowledgments here. However, reference should at least be made to thefollowing names: Dempster, Bennett, Kallmann, Alvarez, Marshall,Woodyard, Herb, Stier, Danforth, and Rose. A number of two-stage tandemaccelerators have been constructed by High Voltage EngineeringCorporation in Burlington, Mass.

By utilizing charge transfer processes in accordance with the invention,three principal advantages are derived therefrom, namely, (1) multipleuse of the available D.C. voltage, (2) an external and grounded ioninjector and (3) the use of multiply charged positive ions.

The limitation on the DC. voltage available is imposed by thesurrounding atmosphere or other insulator between the high voltageportions of the apparatus and the surrounding grounded objects.Atmospheric air can insulate a given voltage, but if this voltage isexceeded one must take special precautions, and the difficultiesencountered increase as the voltage desired increases. For example, onecan enclose the apparatus in a tank filled with gas under pressure inorder to increase the available voltage, but the size of the tankincreases at least with the cube of the voltage. In accordance with thetandem acceleration principles of the invention, it is possible to applythe available voltage which is permitted by the insulation several timesto the same beam of charged particles. In one example hereinafter given,the available voltage may be applied four times to the same beam ofcharged particles.

The second advantage which the invention provides through its use ofcharge transfer processes is that it permits the positioning of the ioninjector outside the high voltage region and at approximately groundpotential. In the conventional D.C. accelerator either the target andbeam analysis apparatus must be at high voltage or else the ion sourcemust be at high voltage. By using charge transfer processes if possibleto have both the ion 'ice source (or particle injector with itsassociated focusing and analyzing apparatus) at earth as Well as havingthe final beam analysis and target apparatus at ground potential. Thiswill be of increasing importance because it enhances the possibility ofutilizing new techniques such as multiple-ion sources, apparatus for thepolarization of particle beams, and equipment for beam pulsing, whichare of tremendous scientific interest.

By using the preferred embodiment of the invention, the ion source is atground rather than within the negative terminal, and this results innumerous advantages. In the first place, no space limitations areimposed on the ion source; in the conventional accelerator, only .1% ofthe total space required is within the high-voltage terminal andavailable for the ion source. In the second place, more power can hedelivered to the source and more heat can be dissipated by coolingapparatus. More information as to the nature of the ion beam isavailable. The ion beam controls can be adjusted more readily;stabilization problems are simplified and, since plenty of power isavailable, standard vacuum tubes can be used in the stabilizationcircuit, and great stability may be obtained using high power RFtechniques; pulsing, beamanalyzing, and diaphragming to selectparticular ions are all rendered more simple. In particular, a verysimple circuit using a photomultiplier may be employed to control thedeflection of the beam so that the beam is always directed precisely atthe canal for charge exchange; such a circuit can have the accuracy of aconventional television-tube cathode ray control. Higher beam currentsmay be obtained by using a plurality of ion sources with convergingoutputs. Moreover, a plurality of ion sources, each providing adifferent type of ion, may be used in succession without dismantling theentire accelerator; thus, one could do four different experiments withtwo generator units and two magnets. As a result of ease of alterationand replacement, the source can be continuoutly improved while in use;the source may be a bench source feeding into a standard high-voltageaccelera tion tube.

The third principal advantage which the invention provides through useof charge transfer processes is that it permits more effectiveproduction and use of multiply charged positive ions. If the electronstripping devices are used in such a way that the positive ions that arecreated are multiply charged, the given DC. voltage can produce manytimes the energy in electron volts than that available with singlycharged positive ions which have been the rule in DC. accelerators. Witha threestage or four-stage tandem accelerator it is possible to obtain agreater yield of stripping than with a two-stage tandem accelerator, sothat greater intensities in the final beam may be obtained for a givenintensity of the beam which is injected into the accelerator. Moreover,with the single stage tandem accelerator of the invention, it

now becomes possible to produce doubly-charged heli-' River accelerator.This 400 kilovolt injector with its power.

supplies, vacuum pumping system, controls and so forth would be far toolarge to install within the terminal of the high voltage accelerator sothat the use of this source of alpha particles is made possible by theuse of the neutral beam of helium particles.

In apparatus embodying the invention, the high-voltage terminals mayderive their potential from any of a number of unidirectional voltagegenerators, such as an electrostatic belt-type generator or atransformer-rectifier set. In the following description thereof, theinvention will be described as making use of an improved form ofelectrostatic belt-type generator; but the invention is not limitedthereto, and the principles of the invention may be applied with equalsuccess making use of other unidirectional voltage generators.

The invention may best be understood from the following detaileddescription thereof having reference to the accompanying drawings inwhich:

FIG. 1 is a diagrammatic view partly in side elevation and partly inlongitudinal central section of a four-stage tandem acceleratorconstructed in accordance with the invention;

FIG. 2 is a transverse section of the column of the apparatus of FIG. 1but showing greater detail and being to a larger scale than that of FIG.1;

FIG. 3 is a diagrammatic view similar to that of FIG. 1 but showing athree-stage tandem accelerator constructed in accordance with theinvention;

FIG. 4 is a diagrammatic view similar to that of FIG. 1 but showing asingle stage tandem accelerator constructed in accordance with theinvention; and

FIG. 5 is a diagrammatic view similar to that of FIG. 1 showing analternative form of four-stage tandem accelerator constructed inaccordance with the invention.

Referring to the drawings and first to FIG. 1 thereof, therein is showna particle accelerator in which the available DC. voltage may be used asmany as four times over on the same charged particle beam. As haspreviously been noted, the available voltage is limited by the breakdownstrength between the high voltage terminal and the surrounding tank.Thus while the length of the device in FIG. 1 is almost six times thatof a single stage accelerator adapted to accelerate to the voltageavailable, the diameter of the device is no greater, so that four foldacceleration is obtained with less than a six fold increase in volume,as contrasted with an increase by four cubed.

Experience in the construction of electrostatic belt-type generators hasshown that the volume of the tank enclosing the insulating gassurrounding the generator and the linear dimensions of the generatorincrease in proportion to more than the cube of the voltage. Theincrease is greater than the cube, due partly to increasing gradientsand partly to the total voltage problem in vacuum tubes. In particular,the column length increases at a rate which is very much greater thanthe voltage. In accordance with the invention, on the other hand, theenergy or equivalent voltage of the accelerated particles is increasedover that obtainable by conventional D.C. accelerators by means of alinear increase in the dimensions of the apparatus.

Although it is possible, without departing from the spirit and scope ofthe invention, to mount a conventional negative ion source within thenegative terminal, in the device shown in FIG. 1 both the originalparticle injector as well as the target and analyzing apparatus are atground potential so that no limitation is imposed on their size. As aconsequence the high voltage terminals may also be smaller since thereis no need to handle the beam source and injection problems. In thedevice shown in FIG. 1 pulleys customarily present in the high voltageterminal have been eliminated and the single belt goes straight throughall the high voltage terminals. Moreover, since the charge particles arenot accelerated in a single long column but rather in a number ofcolumns, the individual columns can be shorter and much smaller indiameter. The columns are shorter because since the total voltage isless, higher voltage gradients can be supported. Since the columns canbe shorter, it follows that they can be smaller in diameter owing tomechanical support considerations. Referring now to FIG. 2 of thedrawing, adjacent equipotential planes of the column and tube areelectrically separated and mechanically supported by only one piece ofglass, whereas in the conventional tandem design, there are five. Thesingle piece of glass or other insulator in practical in the new designof the invention because the acceleration tube occupies a considerablepart of the cross sectional area of the column. All the foregoing showsthat the new electrostatic design of the invention provides a simplerand cheaper construction of the column and terminal.

A further advantage of the electrostatic design of the invention is thefact that in this design a smaller fraction of the radial insulatinglength available for a given tank is lost. That is to say, for a giveninside diameter of the tank there is a certain terminal and columndiameter which provides maximum voltage insulation across the gap. Inconventional devices where the ion source and other apparatus must bestored within the terminal, the diameter of the terminal must be madegreater than the value required simply for high voltage insulation.Thus, for example, the optimum diameter might be 15 inches, and thevarious apparatus required in the high voltage terminal might requirethat its diameter be thirty inches so that one would lose fifteen inchesof insulating region. In fact, in principle the terminal diameter mightbe made even smaller than the calculated optimum for prevention of highvoltage breakdown provided that intermediate shells are used between theterminal and the tank in accordance with my Patent No. 2,230,473, issuedFeb. 4, 1941.

Referring now more specifically to FIGS. 1 and 2, the device thereinshown comprises a tank 1 which is filled with an insulating gas underpressure. Within this tank there is supported a long column 2 which issimilar to that of the conventional electrostatic belt-type generator,except that three high voltage terminals 3, 4, 5 are provided instead ofone. The central high voltage terminal 4 is raised to a high positivevoltage and the other two terminals 3, 5 are raised to a high negativevoltage. Electric charge is deposited and maintained on the high voltageterminals by means of a single insulating belt 6, each end of which issupported on two pulleys 7, 8, 9, 10 rather than one in order that thetwo runs of the belt may be as close together as possible despite thesize of the pulley. The charge transfer is effected by well known chargetransfer devices such as corona discharge and, if desired, both runs ofthe belt may participate in the charge transfer. Thus, for example, ifthe lower run of the belt is travelling from left to right, negativecharge is deposited thereon at ground, and within the first highnegative voltage terminal 3 an appropriate charge transfer device can beprovided which not only removes the negative charge but also sprayspositive charge onto the belt 6 so that in travelling from the firsthigh voltage terminal 3 to the second high voltage terminal 4 the beltbears positive charges. Within the second high voltage terminal thepositive charges are removed and negative charges sprayed on the belt,and these negative charges are then carried by the belt to the thirdhigh voltage terminal 5 where, if desired, positive charge may besprayed on the belt in addition to the removal of the negative charge.This positive charge would then be removed at the grounded pulley.Similar arrangements may be provided on the reverse run of the belt.

It will be observcd from FIG. 1 that, in addition to being supported atits ends, the long column 2 is also supported at the two ground planes11, 12 which are located mid-way between the high voltage terminals 3,4, 5.

At first glance it might be thought that it would be possible to injectpositive ions at the left hand extremity or injection end of theapparatus and accelerate them to the first negative high voltageterminal 3 where they would be converted to negative ions and thenfurther accelerated. Unfortunately the cross section of negative ionformation in this manner falls off rapidly with increasing energy of thepositive ion source above a hundred kilovolts. Such an arrangement isthus inefficient. However,

one can still avoid the necessity of having the original positive ionsource within a high voltage terminal by performing the electron addingprocess in two stages. Accordingly the positive ion source 13 (see FIG.3) is located at ground, but before injection into the accelerator manyof the positive ions are neutralized by the addition to each of a singleelectron. This is accomplished through use of a neutralizing canal 14into which an appropriate gas is introduced for charge-transferpurposes. Although the neutralized beam which emerges from theneutralizing canal has no charge, it nevertheless still has the energyof the positive ion beam, which was given a certain amount ofacceleration upon extraction from the positive ion source 13. As aresult, the neutral beam proceeds at constant velocity up theacceleration tube and into the negative high voltage terminal 3 (FIG.1). Within this high voltage terminal 3 an electron adding canal isprovided. The charge transfer process which take place in this canal issimilar to that which took place in the neutralizing canal 14, exceptthat since the injected particles are already neutral, some of theemergent particles are negatively charged due to having acquired anadditional electron. These negatively charged particles are thenaccelerated from the negative high voltage terminal 3 through the groundplane 11 and into the positive high voltage terminal 4. Electron removalis relatively simple and may be accomplished either by a stripping canalcontaining gas or by a metal foil or other means. Such a strippingdevice H6 is provided within the positive high voltage terminal 4 andconverts the incoming negative ions into outgoing positive ions. Becauseof the ease of electron removal, it is possible at this point in thecase of certain ions to produce multiply charged positive ions by theremoval of several electrons. It is apparent that multiple chargesprovide multiple acceleration for a given voltage drop. The positiveions which are thus formed are accelerated from the positive highvoltage terminal 4 through the second ground plane 12 and into thesecond negative high voltage terminal 4.

One can then put an appropriate target 17 within this high voltageterminal for bombardment thereof by the positive ions. In this Way theaccelerator could be used for the production of artificial radioactivityor in other applications where sufficient detection apparatus of specialdesign could be operated within the high voltage terminal surroundingthe target.

Referring now to FIG. 3 of the drawings, therein is shown anotherembodiment of the invention which although providing few stages ofacceleration than that shown in FIG. 1, has the important advantage ofthe target 18 being at ground. The device of FIG. 3 is identical to thatof FIG. 1, except that there are only two high voltage terminals, thesecond negative high voltage terminal having been eliminated. Forsimplicity of discussion, the single belt 6 has been replaced by twoconventional belts 19, 20; but, of course, the single belt arrangementof FIG. 1 may also be used in the device shown in FIG. 3. In the deviceof FIG. 3, the charged particle injection into the negative high voltageterminal 21 is the same as that in FIG. 1. The negative ions produced inthe negative high voltage terminal are then accelerated through theground plane 22 to the positive high voltage terminal 23 where astripping device 24 is provided for conversion of the negative ions intopositive ions. Here again multiple charging is possible. The positiveions thus created are accelerated to ground and thence into theappropriate beam analyzing devices 25 onto the target 18. The deviceshown in FIG. 3 has three acceleration stages and thus may be called athree-stage tandem accelerator, and it will be observed that the deviceis rendered possible by use of a neutral beam. The formation of theneutral beam is an important part of the invention and plays a part inanother embodiment to be described hereinafter. The neutral beam willenhance the possibility of injecting and acceleration polarizedparticles. It is the use of the neutral beam that permits the ion sourceapparatus to be removed to ground despite the fact that the actual mainacceleration process must start with the production of negative ionswithin a high voltage negative terminal.

Referring now to FIG. 4, therein is shown a device which is essentiallya single stage device. The device therein shown is similar to aconventional electrostatic belttype generator, except that the positiveion source has been removed to earth. This is accomplished by producinga neutral beam such as that produced in the previous drawings anddirecting it into a positive high voltage terminal 26 where a strippingdevice 27 would produce positive ions. One purpose of the device shownin FIG. 4 would be to produce positive ion beams of tremendousintensities-that is to say, much greater than possible with the presentbelt generator, where a representative 3 mev. machine produces a maximumof to 200 microamperes of positive ions. The device of FIG. 4, is, ofcourse, not limited to use with an electrostatic belt-type generator,and much more powerful voltage sources could be used. At the presenttime more power than the electrostatic belt-type generator can provideis not required since the ion source itself provides a limitation.However, using the neutral beam as shown it would be possible to get ionbeams of tens of milliamperes or possibly even hundreds of milliampereswithout the necessity of enlarging the weight to accommodate theconsiderable amount of ion source equipment which would otherwise benecessary. Such intense ion beams could provide, for example, amonoenergetic neutron source of great power. The fact that a beam ofneutral particles has no space charge will be of increasing advantage ashigher particle beam intensities are attempted.

Referring now to FIG. 5 of the drawings, therein is shown what might betermed a four-stage tandem accelerator. It is basically similar to thedevice shown in FIG. 1, except that instead of directing the positiveions from the high positive voltage terminal 4 to a second negative highvoltage terminal 5, they are redirected so that the beam enters thefirst negative high voltage terminal 3 and impinges upon a targetenclosed 28 within it. For this purpose, two magnets 29, 30 or magneticmirrors are provided. As can be seen from consideration of the particleoptics involved, this particular magnet configuration is extremely welladapted for the purpose of redirecting the beam of positive ions asshown. For example, even with small variations in the energy of thepositive ions, the beam will remain parallel to the position shown.

As is shown by FIG. 5, it is not necessary to have the entire apparatusin a single tank, and indeed the multiple acceleration may be providedby the use of several tanks 31, 32. It will be observed that the twotanks in the device shown in FIG. 5 are virtually identical and each inturn is virtually identical to the single stage device shown in FIG. 4.Thus the device of FIG. 4 may readily be converted to the device of FIG.5 by the addition of the appropriate apparatus. Conversely aplural-stage device may be converted to a device of fewer stages throughthe use of appropriate switching arrangements.

It has already been pointed out hereinbefore that by stripping so as toproduce multiply charged positive ions one obtains multiple accelerationfor -a given voltage drop. The number of electrons which are removed bythe stripping process increases with increasing energy of the particlesbeing stripped. The increased particle energy which the inventionalfords for an available voltage thus enhances the possibility ofmultiple stripping. Moreover, in some cases where the stripping devicewithin the high positive voltage terminal can only partially strip theparticles travelling therethrough, it is possible in accordance with theinvention to provide another stripping device in the path of theparticle beam after the particles have acquired additional energy. Forexample, referring to FIG. 5, a foil 33 may be interposed in the path ofthe beam as shown for the purpose of stripping additional electrons withresultant increase in energy gain during the fourth stage ofacceleration.

In the following claims when reference is made to the location of asource of negative ions or to the place at which negative ions areproduced, the location in question is always the point at which the laststep is taken in the production of the negative ions. Thus, the wordsproducing negative ions in a region or the words a source of negativeions within a region includes each one of the following threesituations: (1) direct extraction of negative ions from a dischargewhich takes place within the region; (2) the production of positive ionsWithin the region and conversion thereof into negative ions within theregion or (3) the production of a neutral beam outside the region withthe conversion of said neutral beam into negative ions within theregion.

Having thus described the principles of the invention together withseveral illustrative embodiments thereof, it is to be understood thatalthough specific terms are employed they are used in a generic anddescriptive sense and not for purposes of limitation, the scope of theinvention being set forth in the following claims.

I claim:

1. Apparatus for the acceleration of charged particles comprising asource of low velocity positive ions and a charge neutralizing deviceassociated therewith, a high (with respect to said charge neutralizingdevice) negative voltage terminal having within it an electron addingdevice, a high positive voltage terminal having an electron strippingdevice within it, and means for causing particles originating in saidpositive ion source successively to travel through said chargeneutralizing device, said electron adding device, and said electronstripping device, whereby said particles originating in said positiveion source are neutralized to permit them to reach the high negativevoltage terminal at low velocity, whereby electrons are added to saidneutrals within said high negative voltage terminal so as to formnegative ions which are then accelerated from said high negative voltageterminal to said high positive voltage terminal, and whereby electronsare stripped from said negative ions within said high positive voltageterminal so as to form positive ions which are then accelerated awayfrom said high positive voltage terminal.

2. A method of producing high velocity charged particles, which methodcomprises producing and directing low velocity positive ions,neutralizing some of said pOsi tive ions to form low velocity neutralsof approximately the same velocity and direction, said positive ionshaving been directed so that said neutrals travel across a potentialdifference which is large relative to the potential difference used togive said positive ions their low velocity into a region at high (withrespect to the region in which said positive ions are neutralized)negative potential, adding electrons to some of said neutrals so as toform negative ions, directing said negative ions towards a region ofhigh positive potential, within this region removing electrons from someof said negative ions so as to form positive ions, and directing saidpositive ions away from said region of high positive potential.

3. Apparatus for the acceleration of charged particles comprising anegative voltage terminal having within it a source of negative ions, apositive voltage terminal having an electron stripping device within it,each of said terminals being supported within a grounded tank andmaintained at a voltage with respect to ground which is high relative tothe potential difference used to give said negative ions their velocityat the formation thereof, and means for causing particles originating insaid negative ion source to travel through said electron strippingdevice, whereby said negative ions are accelerated from said highnegative voltage terminal to said high positive voltage terminal, andwhereby electrons are stripped from said negative ions within said highpositive voltage terminal so as to form positive ions which are thenaccelerated away from said high positive voltage terminal.

4. Apparatus for the acceleration of charged particles comprising agrounded source of low velocity positive ions and a charge neutralizingdevice associated therewith. a high negative voltage terminal havingwithin it an electron adding device, a high positive voltage terminalhaving an electron stripping device within it, a grounded target andmeans for causing particles originating in said positive ion sourcesuccessively to travel through said charge neutralizing device, saidelectron adding device, and said electron stripping device, and ontosaid target whereby said particles originating in said positive ionsource are neutralized to permit them to reach the high negative voltageterminal at low velocity, whereby electrons are added to said neutralswithin said high negative voltage terminal so as to form negative ionswhich are then accelerated from said high negative voltage terminal tosaid high positive voltage terminal, and whereby electrons are strippedfrom said negative ions within said high positive voltage terminal, soas to form positive ions which are then accelerated away from said highpositive voltage terminal and onto said target.

5. Apparatus for the acceleration of charged particles comprising asource of positive ions, a charge neutralizing device, a high (withrespect to said charge neutralizing device) positive voltage terminalhaving an electron stripping device within it, and means for directingpositive ions from said positive ion source successively through saidcharge neutralizing device and said electron stripping device, wherebythe positive ions are neutralized to permit them to reach the highpositive voltage terminal, and whereby electron are stripped from saidneutrals within said high positive voltage terminal so as to formpositive ions which are then accelerated away from said high positivevoltage terminal.

6. A method of producing high velocity charged particles, which methodcomprises producing positive ions, neutralizing some of said positiveions to form neutrals, directing said neutrals across a potentialdifference which is large relative to the potential difference used togive said positive ions their velocity into a region of high positivepotential, removing electrons from said neutrals so as to form positiveions, and directing said positive ions away from said region of highpositive potential.

7. Apparatus for the acceleration of charged particles comprising anegative voltage terminal having within it a source of negative ions, apositive voltage terminal having a charge stripping device within it,each of said terminals being supported within a grounded tank and maintained at a voltage with respect to ground which is high relative to thepotential difference used to give said negative ions their velocity atthe formation thereof, means for directing negative ions from saidnegative ion source through said charge stripping device, wherebyelectrons are stripped from said negative ions within said high positivevoltage terminal so as to form positive ions, and means including beamdeflecting fields for directing said positive ions away from said highpositive voltage terminal and into said high negative voltage terminal.

8. Apparatus for the acceleration of charged particles comprising afirst negative voltage terminal having within it a source of negativeions, a positive voltage terminal having a charge stripping devicewithin it, a second negative voltage terminal, each of said terminalsbeing supported within a grounded tank and maintained at a voltage withrespect to ground which is high relative to the potential differenceused to give said negative ions their velocity at the formation thereof,means for directing negative ions from said negative ion source throughsaid charge stripping device, whereby electrons are stripped from saidnegative ions within said high positive voltage terminal so as to formpositive ions, and means for directing said positive ions away from saidhigh positive voltage terminal and into said second high negativevoltage terminal.

9. Apparatus for the acceleration of charged particles comprising anegative voltage terminal having within it a source of negative ions, apositive voltage terminal, each of said terminals being supported withina grounded tank and maintained at a voltage with respect to ground whichis high relative to the potential difference used to give said negativeions their velocity at the formation thereof, means for causingparticles originating in said negative ion source to travel through saidhigh positive voltage terminal, whereby said negative ions areaccelerated from said high negative voltage terminal to said highpositive voltage terminal, and stripping means adapted to remove asufficient number of electrons from some of said particles so that theyhave a plurality of net positive electronic charges while beingaccelerated away from said high positive voltage terminal.

10. Apparatus for the acceleration of charged particles comprising asource of positive ions, a charge neutralizing device, a high (withrespect to said charge neutralizing device) positive voltage terminal,means for directing particles from said positive ion source successivelythrough said charge neutralizing device and said high positive voltageterminal, whereby the positive ions are neutralized to permit them toreach the high positive voltage terminal, and stripping means adapted toremove a sufiicient number of electrons from some of said particles sothat they have a plurality of net positive electronic charges whilebeing accelerated away from said high positive voltage terminal.

11. Apparatus for the acceleration of charged particles comprising ahigh positive voltage terminal, means for injecting particles into saidhigh positive voltage terminal, a stripping device within said highpositive voltage terminal adapted to remove a sufficient number ofelectrons from some of said particles so that they are left with atleast a single electronic net positive charge, and a second strippingdevice posterior to said first stripping device whereby additionalelectrons are removed.

12. Apparatus for the acceleration of charged particles comprising atleast one high voltage terminal supported within a grounded tank andcentrally between the extremities of a column comprising a multiplicityof alternating insulating annuli and apertured equi-potential planes,the apertures within said annuli and within said planes being alignedand evacuated, said annuli and planes being the sole support of thecolumn which includes an endless insulated charge-carrying belt passingthrough the column and operating between grounded pulleys at each endthereof.

13. Apparatus for the acceleration of charged particles comprising atleast one high voltage terminal supported within a grounded tank andcentrally between the extremities of a column comprising a multiplicityof alternating insulating annuli and apertured equi-potential planes,the apertures within said annuli and within said planes being alignedand evacuated, said annuli and planes being the sole support of thecolumn which includes an endless insulated charge-carrying belt passingthrough the column and operating between two grounded pulleys at eachend thereof so that belt spacing is less than the pulley diameter.

14. Apparatus for the acceleration of charged particles comprising atleast one high voltage terminal supported within a grounded tank andcentrally between the extremities of a column comprising a multiplicityof alternating insulating annuli and apertured equi-potential planes,the apertures within said annuli and Within said planes being alignedand evacuated, said annuli and planes being the sole support of thecolumn which includes an endless insulated charge-carrying belt passingthrough the column and operating between grounded pulleys at each endthereof and means for injecting non-positively-charged particles intosaid evacuated region at one extremity of said column.

15. A method of producing high velocity .positive ions by means ofvoltage producing apparatus capable of generating not more than V voltswith respect to ground, which method comprises generating a voltage ofapproximately V with respect to ground at a first terminal, generating avoltage of approximately +V with respect to ground at a second terminal,producing negative ions in the vicinity of said first terminal using avoltage which is low relative to V, directing said negative ion towardssaid second terminal, removing, in the vicinity of said second terminal,electrons from at least some of said negative ions so as to formpositive ions and directing said positive ions away from said secondterminal.

16. A method of producing high velocity positive ions by means ofvoltage producing apparatus capable of generating not more than V voltswith respect to ground, which method comprises generating a voltage ofapproximately V with respect to ground at at least one negativeterminal, generating a voltage of approximately +V with respect toground at a positive terminal, producing negative ions in the vicinityof an aforementioned negative terminal using a voltage which is lowrelative to V, directing said negative ions towards said positiveterminal, removing, in the vicinity of said positive terminal, electronsfrom at least some of said negative ions so as to form positive ions anddirecting said positive ions away from positive terminal towards anaforementioned negative terminal.

References Cited UNITED STATES PATENTS 2,215,155 9/1940 Kallman et al313-63 2,232,030 2/1941 Kallmann et al. 31363 2,272,374 2/ 1942 Kallmanet a1 31363 2,643,349 6/1953 Smith 3105 2,673,928 3/1954 Gurewitsch25027 2,683,216 7/ 1954 Wideroe 25027 2,770,755 11/1956 Good 31363 X2,777,078 1/ 1957 Herchenbach 310-6 2,791,705 5/ 1957 Vieweg 31052,836,759 5/1958 Colgate 31363 X 2,847,586 8/1958 Stiff 31363 2,847,6078/ 1958 Pierce 25027 2,883,606 4/1959 Gale et al 3105 2,890,348 6/1959Ohkawa 25027 2,903,578 9/ 1959 Gallop 25027 3,067,359 12/ 1962 Pottier31363 X 3,136,908 6/ 1964 Weinman 313-63 HERMAN KARL SAALBACH, PrimaryExaminer.

SAMUEL B. PRITCHARD, GEORGE N. WESTBY,

ARTHUR GAUSS, Examiners.

P. D. AMINS, J. W. CALDWELL, D. E. SRAGOW,

S. CHATMON, Assistant Examiners.

1. APPARATUS FOR THE ACCELERATION OF CHARGED PARTICLES COMPRISING ASOURCE OF LOW VELOCITY POSITIVE IONS AND A CHARGE NEUTRALIZING DEVICEASSOCIATED THEREWITH, A HIGH (WITH RESPECT TO SAID CHARGE NEUTRALIZINGDEVICE) NEGATIVE VOLTAGE TERMINAL HAVING WITHIN IT AN ELECTRON ADDINGDEVICE, A HIGH POSITIVE VOLTAGE TERMINAL HAVING AN ELECTRON STRIPPINGDEVICE WITHIN IT, AND MEANS FOR CAUSING PARTICLES ORIGINATING IN SAIDPOSITIVE ION SOURCE SUCCESSIVELY TO TRAVEL THROUGH SAID CHARGENEUTRALIZING DEVICE, SAID ELECTRON ADDING DEVICE, AND SAID ELECTRONSTRIPPING DEVICE, WHEREBY SAID PARTICLES ORIGINATING IN SAID POSITIVEION SOURCE ARE NEUTRALIZED TO PERMIT THEM TO REACH THE HIGH NEGATIVEVOLTAGE TERMINAL AT LOW VELOCITY, WHEREBY ELECTRONS ARE ADDED TO SAIDNEUTRALS WITHIN SAID HIGH NEGATIVE VOLTAGE TERMINAL SO AS TO FORMNEGATIVE IONS WHICH ARE THEN ACCELERATED FROM SAID HIGH NEGATIVE VOLTAGETERMINAL TO SAID HIGH POSITIVE VOLTAGE TERMINAL AND WHEREBY ELECTRONSARE STRIPPED FROM SAID NEGATIVE IONS WITHIN SAID HIGH POSITIVE VOLTAGETERMINAL SO AS TO FORM POSITIVE IONS WHICH ARE THEN ACCELERATED AWAYFROM SAID HIGH POSITIVE VOLTAGE TERMINAL.